Antistatic receiving system



y 14, 1940- w. E. ZUCCARELLO ANTISTATIC RECEIVING SYSTEM Filed Nov. 15,1938 .v m M w ofimww mg @n m m 5 mm w J m 7 AW 0 :33 7mm J Ill PatentedMay 14, 1940 UNITED STATES PATENT OFFICE ANTISTATIC RECEIVING SYSTEMApplication November 15, 1938, Serial No. 240,547

10 Claims.

The present invention relates to radio systems designed to preventinterference from extraneous electrical disturbances, such as staticfrom natural or artificial sources.

In the past, many attempts have been made to eliminate staticinterference from radio receiving systems, but in general these attemptshave culminated in failure due, in a large part, to the fact that theexact character of static impulses has not been sufiiciently taken, intoaccount, nor has the deleterious efiect of these impulses on themodulated carrier been given sufficient consideration. In order that thepresent improvement over existing systems will be thoroughly understood,it is desirable to set forth certain fundamental assumptions, thecorrectness of which has been fully ascertained by elaborateexperiments.

The first of these assumptions is that there is no static that isaudible which decreases the carrier, i. e., a static impulse cannotcause audible decrease of the carrier. Static is not tunable withinpractical limits, because it is highly damped. The static shock-excitesthe tank coils of the coupled circuits, causing continuous waves to beset up therein regardless of the frequency to which the coil is tuned.Individual discharges, such as lightning, last 1 50,000 of a second;therefore, to increase the carrier wave of. a given strength for anaudible period, the impulse would have to heterodyne against thecarrier, beginning as an inaudible heterodyne note, preceeding to anaudible note with a simultaneous decreasein power to an inaudible noteagain, all within 1/50,000 of a second period. The first powerful staticimpulse causes the currents in the tank coil to oscillate in directproportion to the strength of the static which may be many times greaterthan the carrier, causing an audible current to build up of a durationand amplitude sufficient to actuate a speaker diaphragm which vibratesusually long after the initial bulld-up has ceased. Any swing of thetank coil current that is less than the carrier current is immediatelybrought back to carrier strength. by the next carrier oscillation.

Static impulses which are in phase with the carrier do not decrease thevoltage, whereas static impulses which are out of phase tend to reducethe carrier for one cycle, after which the next cycle carrier brings thetank coil current back to the original power. In other words, in orderto receive static, the latter must'be highly damped or it would betunable. To be highly damped, the static must be of short duration andif it is not highly damped, the static causes little or no interference.

The second proven assumption is that, within a given practicable waveband, coupling coils have nearly the same angle of decrement which isevidenced by the same static noise at either end of the band. Decrementdepends upon resistance, coupling and radiation, more than uponcapacity,

in the commercial tank or coupling coils; the

first three are practically the same regardless of capacity. Shorterfrequency tuning radiates more than longer frequencies, but not enoughto make any great change in the angleof decrement.-

invention is based, is that only direct current can successfully bebalanced by grid action or otherwise, and the frequency of the source ofinterference does not necessarily control the audible note. Only theangle of decrement of the static source and the amplification of thereceiver determine the static note or noise.

The final principle on which the present invention is based is thatradio telephony is accomplished commercially by increasing anddecreasing the carrier strength (above and below a mean), but staticenergy is always an increase from zero to maximum and back to zero,never above and below a fixed mean strength. Therefore, to balance suchconditions, only a direct current can be successfully used. Any circuitspurporting touse transformers (audio) or condensers, which tend tocreate or convert to alternating current are impracticable. Any circuitswhich purport to use push-pull transformers or any like arrangement ofbalancing will not balance, due-to the above conditions and the actionof the lines of force in the transformer. Any circuit which uses theautomatic volume control (A. V. C.) feed back of the ordinary type tothe grids of the radio frequency coils merely reduces the strength ofthe signal carrier during a static impulse. If this impulse issufficiently rapid, as in the case of. atmospheric disturbances, theautomatic volume control circuit may cut off the carrier entirely.Hence, there are no means of eliminating the static that fills in thecarrier modulations. Any circuit to filter static can only do so on thefrequency of the filter limits. Any prior circuit that limits themaximum increase over carrier strength distorts the signal, as no methodis used to take out carrier impulses when the carrier is modulated.

Furthermore, any method that purports the balance by the use. of twoseparate receiving channels and does not shape the received power staticto the same characteristics as that static which is impressed on thesignal cannot balance out static on any signal, but can only limit thepower of the static. The stronger the static, the less the balance andthe greater the noise, as the power of the static without the carrierwill cut into the signal strength, causing as much noise on strongsignals or more than static itself on the signal. On weak signals, theoscillograph shows the ear as being deceived and, upon amplification,noise would again be heard under these conditions, because no attempt ismade to cancel the static that is being received during the modulationof the carrier to zero or near zero.

Accordingly, the primary object of the present invention is to simplifythe circuits and apparatus employed in eliminating static from anysource whatsoever.

A more particular object is to provide a radio system which will receivethe static impulses of an audible character together with a modulatedcarrier, but thereafter precludes the static from reaching the telephonereceiver.

A still further object is to cause the audible static impulses to cancelone another within the system. These objects and the manner in whichthey are attained rely for their effectiveness on the four fundamentalswhich have been discussed at length hereinbefore. In brief, I make useof parallel receiving circuits, one of which is adapted to respond to acombined modulated carrier and audible static impulses, the other beingadapted to respond to only audible static impulses and balancing thestatic impulses against one another in a mixer or balancing tube wherebythe static impulses are cancelled.

Other objects and features will be apparent as the specification isperused in connection with the accompanying drawing. This drawing showsa typical electrical system with the tubes diagrammatically illustratedfor carrying my invention into effect.

Referring to the drawing, numeral 1 designates an antenna to groundsystem. Coupled to this antenna through the transformers 2, 3, there area pair of parallelly connected radio receiving circuits which aredesignated circuit A and circuit B, respectively. As will be explainedhereinafter, each of these circuits constitutes a single stage of radiofrequency amplification. a heterodyneoscillator stage, one or morestages of intermediate frequency amplification, and finally a detectorstage. These circuits are identical in construction and arrangement, forreasons which will be stated hereinafter, the only difference being inthe nature of the feed-back circuit or automatic volume controlconnection made to the various stages. Consequently. a descript on ofonly one circuit is necessary, since the other is a duplicate except forthe details mentioned.

The radio frequency stage is preferably constituted of a pentode 4. inwhich the control grid 5 is connected to the tank coil 2 through a variable condenser 6 and a small fixed condenser 1. One terminal of thesecondensers is grounded at 8. The cathode 9 which is indirectly heated bythe filament Ill is connected directly to the suppressor grid II. Thescreen grid !2 is connected to a source of positive volta e indicated bythe terminal l3 which preferably is connected to a tap on a resistorshunted about a double wave rectifier which will be describedhereinafter. The anode i4 is connected through the primary winding of acoil IE to another terminal 1.! of positive potential which is likewiseconnected to a full wave rectifier.

The condensers leading to the grid l2 and the anode I 4 are shunted by apair of fixed condensers I8 to ground so as to prevent radio frequenoycurrents from passing through the terminals l3, l1 into the rectifier.The secondary winding of the transformer i6 is shunted across a variablecondenser l9 and a small fixed condenser 28 to ground at 2| toconstitute a tuned circuit for the input of the oscillator-demodulatingdevice 22. This device is constituted of a combined triode and tetrodeof the ordinary construction. The triode is made up of the cathode 23,control grid 24 and the grid-like anode 25, all of which cooperate toproduce oscillations through the feed-back connection 26, whichoscillations are impressed or combined with the impulses applied to thecontrol grid 2'! of the frequency mixing portion of the tube. Thecontrol grid 21 is preferably enclosed within a screen grid 28 forwell-known purposes and cooperates with the cathode 23 and the anode 29to amplify and mix the received electrical impulses with theoscillations produced in the triode portion of the tube, the cathode 23being prefer ably of the indirectly heated type as indicated.

The immediately associated circuits by which these results are obtainedwill now be described.

The cathode 23 is connected through the usual grid leak resistor 30 andthe condenser 3! to ground at 32 so as to provide the proper bias to thegrids of the heterodyne oscillator. The grid 24 is additionally biasedby means of a grid leak resistor 33 and a condenser 34. The condenser 34is connected through the primary of the feed-back coupling 26 through avariable condenser 35 and a fixed condenser 36 to ground at 37. Thegrid-like anode 25 of the oscillator is connected through the secondaryof the coupling 26 to ground through a condenser 38. A connection fromthis circuit is also made to a terminal of positive potential indicatedat 39 through a resistor 40. The screen grid 28 is connected throughcondenser 4| to a terminal 42 of positive potential. The anode 29 isconnected through a tuned circuit consisting of a variable condenser 43and a transformer primary 44 to a radio frequency choke 45 and thence toa terminal 46 of positive potential. Radio frequency currents areprevented from reaching the terminals 42 and 46 by means of radiofrequency bypass condensers 41 which are connected to ground at 48.

The circuit which has been described up to this point constitutes onestage for radio frequency and a combined oscillator-demodulating stage22, the frequency of which can be adjusted by the variable condenser 35to beat with the incoming frequency impulses applied to the grid 2! andto pass on through the transformer 44 the difference frequency which isconsiderably lower than the radio frequency and is thereafter amplifiedby the intermediate frequency amplifiers to be described presently. Thefirst two stages of the receiving system are of standard type so that noinformation need be given as to the size and adjustments of the variouscondensers. rcsistors. coils, etc., other than to point out that theinput circuits of these sta es are both tuned to the received carrier.and the coupling circuit 43, 44 is tuned to the difference frequencyobtained by the heterodyning action of the tube 22.

The intermediate frequency amplification stage is exemplified by thepentode tube 50. This tube contains an indirectly heated cathode 5|, acontrol grid 52, a screen grid 53, a suppressor grid 54 and an anode 55.The biasing potential for some of these grids is obtained by aresistorcondenser network 56 to ground. The suppressor grid is connecteddirectly back to the cathode.

The control grid 52 is connected through a condenser-transformercoupling circuit indicated generally at to the output circuit of thetube 22. The screen grid 53 is connected to a source of positivepotential 58. The anode is energized by current obtained from theterminal 59 through the primary of the coupling coil (ill. Radiofrequency currents are by-passed around the sources of direct currentpotential by means of condensers 49 connected to ground.

As stated hereinbefore, the purpose of the tube 50 is to amplify thedifference frequencies obtained from the heterodyne tube 22 and to passthese currents on to the detector 6|. This detector may take anysuitable form, but, as illustrated, operates on the dio-detectionprinciple. The diode has an indirectly heated cathode 62, a grid-likeelement 63 which serves the function of the rectifier anode and anelement 66. The secondary of the coupling coil Ell is grounded through afixed condenser 65 and is provided with a variable condenser 66 fortuning purposes. The tuned circuit 65, 66 is made responsive to theintermediate frequency impulses and, by means of a connection 61,impresses these impulses on the element 63. The electrode 64, which isillustrated as an anode, but which simply constitutes the cathode of therectifier, is connected directly to the thermionic cathode 62. Theelement 64 is connected through a condenser-resistor network 68 and aradio frequency choke B9 to the upper plate of the condenser 65. Theelectrode 64 is connected through this network to a tap Hi5 on thenegative side of the resistor 72. This resistor is connected across theoutput circuit of a typical full-wave rectifier l3 which need not bedescribed in detail. Condensers 14 are provided for grounding the radiofrequency currents which might find their way into the rectifyingcircuit. Radio frequency choke coil 15 is provided for a similarpurpose. As Will be noted, an intermediate point on the resistor 72 ofthe rectifying circuit is grounded at Hiso that all potentials taken offfrom points to the left of ground represent the negative potentials, andthose to the right represent positive potentials.

The purpose of the tube 6| is to rectify the incoming waves and, inparticular, to eliminate the carrier so that the potential drop acrossthe network 68 is devoid of carrier, but contains all of the othercomponents including the signal which has been passed through thecoupling circuits of the amplifying and heterodyning stages. Aconnection Iii is taken from a point between the electrode 64 and theresistor of the network 68 to the control grid of a mixer or balancingtube, which will be described presently.

As stated hereinbefore, the circuit B is similar to circuit A, exceptfor a few details which Will be referred to specifically. It is,therefore, unnecessary to duplicate the description of these circuitsand, for convenience in referring to the various elements of the twocircuits, the elements of circuit B have been given the same referencecharacter as the corresponding element of circuit A, except that a smallb has been inserted after the reference character.

The mixer or balancing tube 11 includes an indirectly heated cathode 18,a control grid 19, another control grid 80 which is shielded from thecontrol grid '59 by a screen grid 8|, a suppressor grid 82 .and an anode83. The output currents from the detector SI of circuit Aare conductedto the grid 19 of the mixer or balancing tube Tl. On the other hand, theoutput currents of the detector 61b of the circuit B are taken by theconductor 84 to the control grid 80 of the tube 1?. It will be notedthat the conductor It is connected to a point on the upper side of theresistor-condenser network 68, whereas the conductor 84 is connected tothe lower side of resistor-condenser network 681). Conse- .fixedcondenser 38 and a fixed resistor 89 to the ground terminal 913 on theresistor 72. The purpose of the resistor 89 and this ground connectionwill be described hereinafter.

From a point between the condenser 88 and the plate 83, a connection ismade to a resistor 9!, from which a variable tap 92 is taken to thecontrol grid 93 of an audio frequency amplifier 94. This amplifierincludes an indirectly heated cathode 95 connected through a gridbiasing network 96a to ground. The usual screen grid and suppressorgrids are provided, also an anode 96 which is connected through an audiofrequency coupling 91 to any audio amplifier and receiver arrangementwhich have been merely indicated on the drawing, since theirconstruction is well known.

As stated hereinbefore, the present invention depends for itseffectiveness in removing or cancelling static upon the feature ofbalancing out that part of the static impulses which have been found tobe most deleterious'by way of obje'ctionablc noise in the telephonereceiver. Experiments have shown that that part of the static impulse,which is of greater intensity than the carrier or which in any othermanner overrides the carrier, is the part which is most objectionable.circuits A and B that one of the circuits, for example circuit A, willbe tuned to receive the combined signal-modulated carrier and staticimpulses; whereas the other circuit, for example circuit B, will be soadjusted as to receive only the static impulses which override thecarrier. The difference in adjustment of the circuits which areotherwise identical, except for the detector stage, is brought about byenergy feedback circuits of different character. Thus, in circuit A, theenergy feed-back circuit, which is indicated at 98, is taken from a tapbetween the resistor 89 and the condenser 86 through a re,- sistor 99and a capacity to ground circuit I00 to each of the first three stagesof circuit A.

, Fixed resistors iill are connected between the input tuned circuits ofthe tubes 4 and 22 to the conductor 98 so as to prevent inter-tubeoscillation. A direct connection is made between the input circuit ofthe tube 5i and. the conductor 98 to a point between the resistor 99 andcondenser ltd. On the other hand, the feed-back connection Hi2 incircuitB is passed through a radio frequency choke 1% to the various stages. Itwill be noted that each of these feed-back connections originates fromthe same point in the anode circuit of the balancing tube 11, so thatthe same components flow through these circuits, except such that areprevented or otherwise attenuated by the resistor Bil-condenser I'illlnet- For that reason, I propose to so adjust the i carrier takes placein the tube 71.

work in Circuit A, and the radio frequency choke H13 in circuit B.

These attenuating elements affect the feedback energy in a differentmanner so that the feed-back current or voltage impressed on the variousstages of the two parallel circuits is of a different biasing characterand magnitude. It is apparent that the nature and adjustment of theseelements can be controlled in such a way that the difference in thecharacter of the feedback current or voltage will discriminate betweenthe circuits A and B as to their respective amplifying properties. Usingthe elements, as illustrated, I have found that it is feasible to reducethe amplifying property of circuit B, for example, to such an extentthat it will respond to antenna energy only above a predeterminedamount, at the same time leaving circuit A with its full or otherdesired amplification. This circuit A will be permitted freely torespond to modulated carrier and static, whereas circuit B will bebiased to such an extent that it will respond only to static above apredetermined intensity level, for example, above carrier strength.

Consequently, the grid 19 of the balancing tube receives from circuit A,combined signal and static impulses (the carrier has already beeneliminated in the detector 6!) and the grid 80 receives only staticimpulses greater than carrier intensity from circuit B. The effect ofstatic on grid 80 is opposite to the efiect of the static component ongrid 19, because as one grid is driven negative, the other is drivenpositive with respect to the cathode. This is due to the fact that theconductor 10 is connected to the opposite side of the network 68 fromthe side to which conductor 84 is connected to its network 68b. Thus, acancellation or balancing out effect of static impulses of greaterintensity than the In order to prevent inter-electrode capacity errors,the grids T9 and 80 are shielded from one another by the screen grids8|.

The grid 19 of the tube T1 is preferably biased by means of the tap I sothat the tube will cut off when there is no signal. It will be notedthat the plate 33 is connected to ground through the resistor 9| sothat, when no signal current is passing through the tube, the plate ismaintained at zero potential. On the other hand, when signal currentsare flowing, the plate is maintained at negative potential due to thedrop in the resistor. Thus, the tube 11 is maintained in a highlysensitive condition between signals.

The current which is fed to the input circuit of the audio frequencyamplifier 94, through the tap 92, is devoid of static, at least of thatstatic which is of greater intensity than the carrier and which normallyis most objectionable in the telephone receiver. The static which is ofless intensity than the carrier is not so harmful from the auditorystandpoint, since it does not mask out the signals or speech to anygreat extent and readily permits discrimination at the receiver.

By providing two parallel circuits, stages of which are substantiallyidentical, assures that the same electrical actions are performed by thetubes and their various coupling circuits including the tank coils onthe static in both circuits. Consequently, the balancing tube receivestwo static impulses of exactly the same wave shape, which can completelycancel one another. It will be noted that the concellation of the staticimpulses is performed solely by the use of direct currents in thebalancing tube and, therefore, en-

tails the only practical way in dealing with static as is fullydiscussed under the fourth assumption set forth at the beginning of thespecification.

In order that the grids l9 and 80 will have the same effect, but in theopposite sense, on the electron stream in the balancing tube,notwithstanding their difference in position with respect to thecathode, the bias on these respective grids is maintained at differentvalues and controlled by the tap 'H which is connected through theresistor of the network 6822 to the grid 80.

Modifications of the system which has been shown and described willreadily occur to those skilled in the art. For example, the detectorsiii and Gib may be combined in one envelope and any number of high andintermediate radio frequency stages employed, indeed, other wellknownforms of receiving circuits could be used to advantage, provided thesecircuits lend themselves to automatic volume control feed-back whichwill selectively control the amplifying properties of the two circuits,and in that manner cause one of the circuits to respond to thedeleterious impulses which are eventually cancelled out in the balancingtube.

Consequently, it will be understood that I desire to comprehend withinmy invention such modifications as come within the scope of the claimsand the invention.

Having thus fully described my invention. what I claim as new and desireto secure by Letters Patent is:

1. A static eliminating system comprising two receiving radio circuits,one of said circuits comprising means for receiving combinedsignalmodulated carrier and static impulses, the other circuitcomprising means for receiving static impulses only of greater strengththan the carrier, means for differentially balancing the output currentsof one circuit against the output currents of the other circuit, wherebythe static impulses of greater strength than the carrier are removed,and means for amplifying the differential currents.

2. A static eliminating system comprising two receiving radio circuits,means for tuning one of said circuits to respond to the combined signalmodulated carrier and static impulses, means for adjusting the othercircuit to respond only to the static components of greater strengththan the carrier, means for separating the signals from the carrier butleaving in the static impulses, a bal ancing'tube for combining theoutput currents of the circuits in a differential manner, whereby thestatic impulses of greater strength than the carrier are removed fromthe signal, and means for receiving the output currents of the balancingtube.

3. A static eliminating system comprising two parallel heterodyne radioreceiving circuits, each including a detector, a balancing tube fordifferentially combining the output currents of said circuits, meansincluding automatic volume control circuits connected between the outputcircuit of said balancing tube and said receiving circuits for causingone of the receiving circuits to respond to combined signal-modulatedcarrier and static impulses and to cause the other of said receivingcircuits to respond to static impulses which override the carrier,whereby the output circuit of said balancing tube contains no static ofgreater intensity than the carrier, and means for translating the outputcurrent of the balancing tube into sound undulations.

4. A static eliminating system comprising two parallel heterodyne radioreceiving circuits, each including a detector, a tube for balancingpredetermined components of the output current of one of said circuitsagainst similar components of the output current of the other of saidcircuits, means for feeding back energy from said tube to one of thereceiving circuits, said energy being of a biasing character to permitits receiving circuit to respond to the combined signal-modulatedcarrier and static impulses, means for feeding back energy from saidtube to the other of said receiving circuits, said energy being of abiasing character to permit its receiving circuit to respond only tostatic impulses which. override the carrier, whereby the audible staticimpulses are balanced out in said tube, leaving only the signalcomponent, and means for translating the signal component into audibleundulations.

5. A static eliminating system comprising two parallel radio receivingcircuits, each including a plurality of tube elements of similar numberand character, means for adjusting one of said circuits to receivecombined signal-modulated carrier and static impulses, means in said onecircuit for eliminating the carrier, means for adjusting the other ofsaid circuits to receive only the static impulses which override thecarrier, means for balancing the audible static currents in one circuitagainst the audible static currents in the other circuit, whereby thedeleterious static impulses are removed from the signal, and means fortranslating the signal impulses into sound undulations.

6. A static eliminating system comprising two parallel radio receivingcircuits, each including a plurality of tube elements of similar numberand character, means including a feed-back connection for adjusting oneof said circuits to receive combined signal-modulated carrier and staticimpulses, means in said one circuit for eliminating the carrier, meansincluding a feedback connection for adjusting the other of said circuitsto receive the static impulses which override the carrier, means forbalancing the audible static currents in one circuit against the audiblestatic currents in the other circuit, whereby the deleterious staticimpulses are removed from the signal, and means for translating thesignal impulses into sound undulations.

7. A static eliminating system comprising two parallel radio receivingcircuits, each including a plurality of tube elements of similar numberand character, one of said circuits comprising means for receiving thecombined signal-modulated carrier and static impulses and the other ofsaid circuits comprising means for receiving only static impulses whichoverride the carrier, a detector tube in each of said circuits, meansfor balancing the output static currents from one detector against theoutput static currents from the other detector, said balancing meanscomprising a balancing tube having an anode and a plurality of grids,said output static currents being applied in a difierential manner tosaid grids, whereby signal currents appear in the anode circuit of thebalancing tube, and means for translating the signal currents into soundundulations.

8. A static eliminating system comprising two parallel radio receivingcircuits, each including a plurality of tube elements of similar numberand character, one of said circuits comprising means for receiving thecombined signal-modulated carrier and static impulses, and the other ofsaid circuits comprising means for receiving only static impulses whichoverride the carrier, a detector tube in each of said circuits, meansfor balancing the output static currents from one detector against theoutput static currents from the other detector, said balancing meanscomprising a balancing tube having an anode and a plurality of grids,said static currents being applied in a differential manner to saidgrids, whereby signal currents appear in the anode circuit of thebalancing tube, one of said grids being biased to cut off the anodecurrent in said balancing tube when no signal passes through thedetector tube of that circuit which responds to the combinedsignal-modulated carrier and static impulses, and means for translatingthe signal currents into sound undulations.

9. A static eliminating system comprising two parallel radio receivingcircuits, each including a plurality of tube elements of similar numberand characteristics, one of said circuits comprising means for receivingthe combined signalmodulated carrier and static impulses and the otherof said circuits comprising means for receiving only static impulseswhich override the carrier, a detector tube in each of said circuits,means for balancing the static tube currents from one detector tubeagainst the static output currents from the other detector tube, saidbalancing means comprising a balancing tube having an anode and aplurality of grids, said static output currents being applied in adifi'erential manner to said grids whereby signal currents appear in theanode circuit of the balancing tube,

one of said grids being biased to cut ofi the anode current in saidbalancing tube when no signal passes through the detector tube of thatcircuit which responds to the combined signal-modulated carrier andstatic impulses, the anode of the balancing tube being maintained atzero potential when no signal is passing through the detector tube ofthat circuit which responds to the combined signal-modulated carrier andstatic impulses but automatically being biased negatively when signalimpulses are passing through the detector tube of that circuit whichresponds to the combined signal-modulated carrier and static impulses,an energy feed-back connection from said anode to each of said receivingcircuits to adjust one of said circuits to respond to the combinedsignal-modulated carrier impulses and to adjust the other of saidcircuits to respond only to static impulses which override the carrier,whereby the impulses applied to one of the grids of the balancing tubeare constituted of signals mixed with static and the impulses applied tothe other grid of the balancing tube are constituted solely of static sothat the differential effect of these grids is to balance out staticabove a predetermined intensity, leaving only the signal currents andstatic below said predetermined intensity, and means for translating thesignal currents into sound undulations.

10. In a static eliminating system, the method of receiving a combinedsignal-modulated carrier and a static wave, comprising removing thecarrier by detection, simultaneously receiving static impulses of onlygreater intensity than said carrier, then balancing the static componentof the received impulses against the static impulses to remove thestatic of greater intensity than the carrier and leave the signal withstatic of less than carrier intensity, and finally translating thesignal into sound undulations.

WILLIAM E. ZUCCARELLO.

